I think that nestlings have hatched. Harriet is more vocal and no longer lies low and flat; most of the time, she hunches over something(s) now.
Also, Ozzie is spending more time near and on the nest:
I can’t peer into the nest, so I’ll have to wait until the nestlings get near an edge (if there are nestlings) to see them. It’s time for them, I think! (Images taken in Brooklin, Maine, on June 16, 2023.) See also the image in the first Comment space.